Honda BF-75 4-stroke - Carburator question

Hi All!



Just bought an old engine - A 4 stroke Honda BF-75 engine. At first it was almost impossible to start, but after taking apart the carburator (named 268a - see image) it starts very easily, and runs fine up until aprox 75% of full power. But if giving more gas the engine runs really bad and almost stops.

I´m not much of a engine guy, so I´d though I´d ask some questions related to the images.

- 1st of all, what does the lever marked "A" do. "B" and "C" is throttle and choke. A should be connected to the part where I connect the fuel (See image) but that connector is broken.

- Secondly I wounder if you have any ideas of what can cause the problems I´m seeing.

Thanks
Thomas

Is it likely that bad sparkplugs would cause this? I´m thinking as it runs very smooth on less than 50% power, then the sparkplugs would work good enough?

Secondly I was thinking if it could be due to a bad fuelpump, but I´ve tested it seems to pump fuel ok. I don´t expect it to have to pump with a huge pressure - do I?

I am pretty sure that "A" is a fuel cut off valve. Since the linkage is broken from where you connect the fuel, it may be partially closed and cutting off the amount of fuel that the carburetor gets at full throttle. When the fuel connector is removed, the valve is supposed to close.

You should not have to pump at a high pressure. The fuel pump only puts out 3 - 4 psi. It could be a restriction in the fuel line...if the motor does not run better when you pump the bulb, there probably is not a restriction.

Try pulling the choke out various amounts (just a little, a lot , etc) and see if the engine picks up. If so....relook at the carb.

It could also be bad spark plugs, but you will not know until you change them.

It could also be the timing belt has jumped a notch on the flywheel or cam. Make sure the alignment marks line up.

It could also be that you have not completely cleaned the carburetor....although, there are not a lot of intricate passages in this carb.

Check compression to be sure there is no cylinder issues.

One last thing are you using the correct fuel connector? It may look like an Evinrude connector, but it will not fit correctly.

Make sure it is the Honda fitting. 17650-921-003ZB

Good luck....

Mike